Re: [Xen-devel] [PATCH RFC v1 41/74] xen/pvh: do not mark the low 1MB as IO mem

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.01.18 at 14:05, <wei.liu2@xxxxxxxxxx> wrote:
> @@ -288,8 +289,12 @@ void __init arch_init_memory(void)
>      dom_cow = domain_create(DOMID_COW, DOMCRF_dummy, 0, NULL);
>      BUG_ON(IS_ERR(dom_cow));
>  
> -    /* First 1MB of RAM is historically marked as I/O. */
> -    for ( i = 0; i < 0x100; i++ )
> +    /*
> +     * First 1MB of RAM is historically marked as I/O.  If we booted PVH,
> +     * reclaim the space.  Irrespective, leave MFN 0 as special for the sake
> +     * of 0 being a very common default value.
> +     */
> +    for ( i = 0; i < (pvh_boot ? 1 : 0x100); i++ )
>          share_xen_page_with_guest(mfn_to_page(_mfn(i)),
>                                    dom_io, XENSHARE_writable);

I can see this being valid as long as there's no firmware. What
doesn't become clear from neither the description nor the
comment is whether this is a necessary change, or just an
optimization to avoid wasting these 255 pages.

Jan


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